Project Summary/Abstract Immunotherapies designed to stimulate anti-tumor immune responses by enhancing CD8+ T-cell activity have revolutionized the treatment of cancer, but many patients do not respond. Robust CD8+ T-cell recognition of tumors requires the presentation of cellular antigens on Major Histocompatibility Complex I (MHC-I) and many cancers suppress MHC-I presentation as a means of evading immune detection and acquiring resistance to immunotherapy. This proposal outlines experiments to explore a mechanistically distinct method of stimulating antigen presentation by disrupting protein-folding pathways. The heat shock protein 90 kDa (HSP90) is a molecular chaperone that is known to regulate the stability of numerous cellular proteins, termed HSP90 ?clients?, including proteins involved in oncogenic signaling pathways. Perhaps most interestingly, HSP90 is particularly important for maintaining the conformational stability of mutated proteins. Therefore, inhibition of HSP90 function represents a unique strategy for destabilizing the mutant proteomes of cancer cells to reveal them to the immune system. While numerous HSP90 inhibitors have been tested clinically as a means to disrupt oncogenic signaling and kill cancer cells, none have been FDA approved. Preliminary data demonstrate that in contrast to clinically tested dosing strategies, continuous, low dose exposure to HSP90 inhibitors stimulates MHC-I antigen presentation and drives anti-tumor immune responses in a syngeneic mouse model through a mechanism that is fundamentally distinct from high dose HSP90 inhibitor treatment. However, the mechanism of MHC-I induction and the relationship between HSP90 clients and MHC-I antigens is unknown. Using pharmacological, genetic, and proteomic tools, this proposal will uncover the mechanism driving MHC-I induction following low dose HSP90 inhibitor treatment. Furthermore, experiments in genetically engineered mouse models of lung adenocarcinoma and colorectal cancer will investigate the consequences of this treatment strategy on antigen presentation and anti-tumor immune responses in vivo. Taken together, this study will evaluate low dose HSP90 inhibition as a mechanistically distinct method to induce MHC-I antigen presentation and reveal mutated cancer cell proteomes to the immune system, and also provide support for repurposing orally bioavailable HSP90 inhibitors as a new class of immunomodulatory agents. This proposal also outlines career objectives and goals in preparation for obtaining a faculty position. Notably, the career development plan identifies key areas for training in tumor immunology, animal modeling, mentorship of trainees, and oral and written scientific communication. The training activities are designed to build skills, both scientific and professional, that are required for running an independent laboratory. Finally, the complementary expertise of the co-sponsors, the advisory team, and rich scientific environment at MIT are uniquely suited to ensure success of the proposed research and career development goals. !